How long does opened pasta sauce last in the fridge?

Short answer: an opened jar of plain tomato pasta sauce, kept cold, is generally good for around five to seven days — noticeably shorter than the ketchup sitting next to it in the door, and shorter still once meat, cream or fresh cheese has been stirred in. The confusion is understandable. Pasta sauce looks like the same category of thing as ketchup — a red, acidic, jarred tomato product — but it is made to a different recipe, and that recipe is exactly what decides how much margin you actually have.

Why it is not ketchup in a bigger jar

Ketchup keeps for months after opening because its formula is built around preservation as much as flavour: a high concentration of vinegar and sugar alongside the tomato, which between them starve and repel most of what would otherwise spoil it. Pasta sauce is built around a completely different goal — tasting like tomatoes, garlic, herbs and olive oil, not lasting on a shelf. It carries real acidity from the tomatoes themselves, which is genuinely protective and is why a jar of plain marinara outlasts, say, an opened carton of stock. But that acidity sits well below ketchup's, because nobody wants a bowl of pasta to taste like a condiment. Less vinegar and sugar means less of the preservation effect that vinegar and sugar provide, and that is the entire difference in a sentence.

What actually decides the window

What is in the jar besides tomato. A plain tomato-and-herb sauce is the longest-lasting version, because tomato acidity is doing most of the work and there is little else in there to spoil. Add meat and the sauce inherits meat's much shorter, higher-risk shelf life — a bolognese behaves like leftover cooked meat, not like a jarred condiment, and belongs in the three-to-four-day range that applies to cooked meat generally. Add cream or fresh cheese and the same logic applies from the dairy side: a vodka sauce or a carbonara-style jar is only as good as the cream in it, which is a matter of days, not a week.

Homemade versus store-bought. A commercial jar has usually been heat-processed and sealed in a way that gives it a real margin before it was ever opened, on top of the tomato's own acidity. A pot of homemade sauce cooling on the stove never went through that step. It is, food-safety-wise, simply a cooked dish — closer to leftover soup than to a shelf-stable jar — and it is worth treating it on the same clock as any other cooked leftover: refrigerated within about two hours of cooking, and used within three to four days, regardless of how tomato-forward the recipe was.

How the jar gets used. A spoon that went from the pot into the jar and back into the pot carries a little of whatever was cooking with it. A clean utensil each time, and getting the jar back into the fridge promptly rather than leaving it out on the counter through a whole meal, both genuinely extend the window — the same rule that applies to every other opened jar in the fridge.

What to actually look for

The signs worth trusting are the same ones that apply across the whole fridge, not a special pasta-sauce checklist.

• Any mould, anywhere on the surface, means the whole jar goes. Sauce is wet and loose enough that mould's roots reach further into it than the visible spot suggests — scooping around a fuzzy patch does not remove what is actually growing underneath it.
• A bulging lid or fizzing when opened is a fermentation sign, not a quality one. That points to gas being produced inside the jar, which is not something a spoonful of extra herbs is doing.
• A sharp, sour, or off smell that goes beyond ordinary tomato tang is worth trusting over the calendar. Tomato sauce already smells acidic; the change you are checking for is a shift into something unpleasant, not the baseline tang itself.
• A darker layer on top, or a little separated liquid, is usually just oxidation and settling. Stirring it back in and checking smell and appearance normally settles the question — this is a texture change, not the same thing as mould or fizzing.

What actually helps

• Write the day you opened it, not the day you bought it. A jar that sits in the door for weeks unopened tells you nothing about how long it has been open — that is the date that actually matters.
• Move a jar with meat or cream in it out of the "long-lasting condiment" mental bucket. Treat it like the leftover dish it actually is, not like the ketchup it is sitting next to.
• Decant leftover homemade sauce into a clean container rather than leaving it in the cooking pot. A pot cools more slowly in the middle, which is exactly the temperature range spoilage organisms like best.
• Freeze what will not be used within the week. Tomato-based sauce freezes well in flat bags or portioned containers, which turns "use it in five days or lose it" into "use it whenever the next pasta night happens to land."

This is really the same distinction Munch is built to keep straight without you having to hold it in your head: marking a jar opened switches it onto its own shorter countdown from that day, separate from whatever was printed for the sealed jar, and a homemade batch logged the day it was cooked carries its own leftover-length window rather than quietly borrowing a jarred sauce's reputation for lasting forever.

The short version to actually remember: tomato acidity buys real time, but it is not the same acidity ketchup runs on, and anything added on top of the tomato — meat, cream, fresh cheese — shortens the window to match whatever was added, not the other way around.